Prioritization of the Secondary Metabolites for the Rapid Annotation Based on Liquid Chromatography-High Resolution Mass Spectrometry Assessment: Varanasine and Schroffanone from Murraya paniculata and Cytotoxic Evaluation

The liquid chromatography-high resolution
mass spectrometry (LC-HRMS)
technique enables the detection of phytochemicals present in the extracts.
LC-HRMS-generated mass list showed abundant compounds of interest,
artifacts, and primary metabolites. The identification of a secondary
metabolite of interest within the extract is very challenging. We
hypothesized that identifying the “new metabolite” in
the whole metabolome is more challenging than identifying it within
the class of metabolites. The proposed prioritization strategy focused
on the elimination of unknown and prioritizing the known class of
secondary metabolites to identify new metabolites. The prioritization
strategy demonstrated on Murraya paniculata for the identification of new metabolites. LC-HRMS-generated information
is used as a filter to target the secondary metabolite and the new
metabolites. This strategy successfully annotated the new coumarin
and coumarin alkaloids from the mass list of 1448 metabolites. Varanasine
(3), schroffanone (4), schroffanene (5), and O-methylmurraol (9)
are new compounds, and coumarin (1, 2, and 6–8) are known. Varanasine (3) is the
first naturally occurring 7-aminocoumarin with additional N-formyl functionality. The isolates were screened for cytotoxicity
against the panel of cancer cell lines. Varanasine (3) and minumicrollin (6) showed significant cytotoxicity
and apoptosis-inducing potential. The immunoblot analysis confirmed
inhibition of apoptotic protein PARP-1 and caspase-3 expression by 3 and 6.